How to show a message, redirect user, and generate PDF in the background?

I need to implement a flow where, when a user clicks the “Generate PDF” button, a message appears saying “Your PDF is being generated,” and the user is redirected to the homepage. Meanwhile, the PDF generation continues in the background on the server.

I’m using JavaScript for the frontend and PHP on the backend. The PDF generation may take some time, so I want to ensure the user isn’t blocked during this process. I plan to send an asynchronous request to start PDF generation and then redirect the user. On the backend, I want to run the PDF generation in the background (via a worker or exec()).

What’s the best approach to implement this without blocking the user’s experience?